Light processing device utilizing beamsplitter having first region reflective from both sides and second region which is transparent

ABSTRACT

Disclosed is an interferometer using therein a beamsplitter having a thin-film, transparent substrate; a plurality of stripes, each stripe being reflective from both sides and affixed to the substrate; and two mirrors positioned such that as a wavefront of light is divided by the beamsplitter, the divided beams impinge upon the mirrors, whereby when one mirror is moved toward or away from the beamsplitter, the beams impinging upon the movable mirror are changed in phase from the beams impinging upon the other mirror, the phase being measured by a light detector.

United States Patent Reid et al. 1 June 6, 1972 [54] LIGHT PROCESSINGDEVICE [56] References Cited UTILIZING BEAMSPLITTER HAVING UNITED STATESPATENTS FIRST REGION REFLECTIVE FROM BOTH SIDES AND SECOND REGION587,443 8/1897 Konig ..350/172 R IRE 1,603,331 10/1926 Downey.....350/l72 WHICH IS T SP NT 1,662,693 3/1928 Astafiev ..350/172 [72Inventors: Lee R. Reid, Richardson; Charles Sumner 2,151,631 3/1939Williams ..356/1l3 Williams, Dallas, both of Tex.

' Pnmary Examiner--James W. Lawrence [73] Assignee. $eias InstrumentsIncorporated, Dallas, Assistant N. Grigsby e Attorney-Samuel M. Mimms,Jr., James 0. Dixon, Andrew [22] Filed: Nov. 16, 1970 M. Hassel, HaroldLevine and John E. Vandigrifi 1] Appl. No.: 90,143 [57] ABSTRACT RelatedJ's-Application Data Disclosed is an interferometer using therein abeamsplitter [63] Continuation of No 757,371 Sept. 4 1968 having athin-film, transparent substrate; a plurality of stripes, abandoned eachstripe being reflective from both sides and affixed to the substrate;and two mirrors positioned such that as a wavefront 52 us. 01. ..250 220s1), 350 172, 356/13 of light is divided y the beamepliiter. the dividedbeams p- 51 Int. Cl. ..G01c 3414,0021) 27/14,I-101j 39 12 s p themirrors, whereby when one mirror is moved 58 Field of Search..356/13,'106;350/172; toward or y from the beemspliner. the beamsimpinging 250/220 SD upon the movable mirror are changed in phase fromthe beams impinging upon the other mirror, the phase being measured by alight detector.

6 Claims, 4 Drawing Figures MIRROR MOVEMENT PATENTEDJHH 6l972 3,668,406

SHEET 20F 3 MIRROR MOVEMENT V l6 l7 PROCESSOR LIGHT PROCESSING DEVICEUTILIZING BEAMSPLITTER HAVING FIRST REGION REFLECTIVE FROM BOTH SIDESAND SECOND REGION WHICH IS TRANSPARENT This application is acontinuation of my prior application Ser. No. 757,371, filed Sept. 4,1968, now abandoned.

This invention relates to improvements in optical devices and moreparticularly to a new thin-film, wavefront-dividing beamsplitter.

In general, a beamsplitter is a device which divides (or splits) a beamof light incident upon it into two portions, ideally each portion beingof equal strength or amplitude. For example, most commonly usedbeamsplitters comprise a surface having particular optical propertieswhich make the surface half reflective and half transmissive to a beamof light incident upon it, so that when a beam of light does impinge onthe surface, one-half of it passes through the beamsplitter, and theother half is reflected. Generally, if the beamsplitter is positioned atan angle of 45 to an impinging beam of parallel rays, as from a lightsource at infinity, for example, the reflected and transmitted beamswill be at an angle of 90 to each other.

Beamsplitters are most commonly used in interferometers, devices whichutilize the phenomena of light interference for precise determinationsof wave length, spectral fine structure, indices of refraction, andsmall linear displacements. When used in an interferometer, thebeamsplitter is used in conjunction with reflecting surfaces, one ofwhich can be moved such that the phase of one beam can be modified withrespect to the other beam, so that changes in the relative phasedifference between the two waves can be determined. In a commonly usedinterferometer, a mirror is provided for each beam to reflect it back tothe beamsplitter at such an angle that after being again reflected fromor transmitted through the beamsplitter, the two beams, initially at anangle of 90 to each other, travel in parallel paths, thus enabling theirrelative phase difference to be determined.

In operation, the portion of the beam which was first reflected from thebeamsplitter is reflected by a first reflective surface back onto thebeamsplitter where it is again divided. Upon again being divided, onehalf of the twice reflected light then passes through the beamsplitterin the direction of a detector and one half is reflected toward theoriginal light source. The beam of light which was first transmittedthrough the beamsplitter is reflected by a second reflecting surfaceonto the back side of the beamsplitter, one half of the beam then beingreflected to the detector in a path parallel to the first reflectedbeam, and one half being transmitted toward the original light source.The second reflecting surface is generally linearly movable towards andaway from the beamsplitter to change the phase of the first transmittedbeam from that of the first reflected beam by a measured, proportionalamount. One use of the apparatus, therefore, is to determine lengths ofobjects very accurately which otherwise could not be physicallymeasured, or it can be used in many other so-called ray errormeasurements.

Although the merits of the partially-reflecting beamsplitter abovebriefly described are abundant, it nevertheless has severaldisadvantages. In the above description, for example, the light which iseither reflected or transmitted in the direction of the initial lightsource is wasted. The maximum theoretical efficiency of the beamsplitteris, therefore, 50 percent, and actual efficiencies are much lower on theorder of 6 percent to 11 percent.

Also, the bandwidth, the range of wavelengths of light that theabove-described beamsplitter will pass without substantially reducingthe output amplitude, is limited, mainly because of light absorptionwithin the beamsplitter material. Furthermore, the commonly usedbeamsplitters are incapable of passing light in the infrared wavelengthrange. This limits their use in interferometer spectrometers, as moreparticularly described below.

Finally, in most partially reflecting beamsplitters, compensator platesare required, since light waves when passing from one medium to another,change velocity and direction. This is demonstrated by the familiarexample of looking at a fish in a pond: the fish appears to the observerto be in a position lower than it actually is because of the differencein velocity of light waves in air and in water. Most partiallyreflecting beamsplitters have a thickness which is longer than a singlewavelength of light. The change in velocity is different for difierentwavelengths so that the optical path difference between the two beams(the reflected and transmitted beam) varies with wavelength. The purposeof the compensator plate is to introduce the same change in velocityalong equal distances for the two beams.

Accordingly, it is an object of the invention to provide a beam-splitterwhich has an increased efficiency.

It is a further object to provide a beamsplitter which has a relativelywide bandwidth.

It is yet a further object to provide a beamsplitter which can be usedin interferometer spectrometers operated at wavelengths in the infraredregion of the electromagnetic radiation spectrum.

It is a still further object to provide a beamsplitter which does notrequire the use of a compensator plate.

Other objects, features and advantages of the invention will becomeapparent to those skilled in the art from the following detaileddescription when read in conjunction with the appended claims andattached drawings.

FIG. 1 is a plan view of one embodiment of the beamsplitter of theinvention;

FIG. 2 is a cross-sectional view along line 2-2 in FIG. 1 of a cut-awayportion of the mounting ring, pellicle and reflecting stripes used inthe beamsplitter of the invention;

FIG. 3 is a diagrammic view of the beamsplitter used in conjunction withreflective surfaces for use in applications such as in interferometers;and

FIG. 4 is a diagrammic view of a cut-away portion of the beamsplitter ofthe invention showing the geometrical considerations involved indetermining the size and spacing of the reflective stripes.

In accordance with the present invention, a beamsplitter is presentedwhich, unlike the above-described partially reflecting beamsplitter,operates on the theory of wave front division. Whereas in the partiallyreflective beamsplitter the incident beam is divided by amplitude. Thebeamsplitter of the present invention operates on the wavefront divisiontheory, that is, the incident wave is divided into two beams, oneentirely reflected and one entirely transmitted through thebeamsplitter.

The beamsplitter of the invention achieves the wavefront division of abeam of light by a series of stripes, each being reflective on bothsides, mounted on a thin transparent substrate, such as a thin filmpellicle. Hence, as a light wave is incident upon the beamsplitter, thatportion of the wave incident on the reflective stripes is entirelyreflected and that portion which is incident on the pellicle is entirelytransmitted therethrough. When used in an interferometer, widths of thereflective stripes and the distances between each of them can bearranged so that the two beams created by the beamsplitter can bereflected back to the beamsplitter by two mirrors, and, theoretically,all of the light of both beams is redirected by the beamsplitter intoparallel paths in the direction of a light detector to record theintensity of the combined beams. Since light waves of different phaseinterfere additively or subtractively to make a light beam having itsamplitude determined by the amount of phase difference, a lightamplitude detector may be used.

The base of the beamsplitter of the invention is a mounting ring 10 of,for example, quartz or other suitable material. Constructed on thequartz ring is a thin film pellicle 11, for example, a transparentmembrane of a nitrocellulose base material. One method of constructing asuitable thin film pellicle of thickness, for example, of 0.3 to 3.1microns is described in copending application, Ser. No. 497,294 now U.S.Pat. No. 3,438,694, filed Oct. 18, 1965, entitled Beam Splitter", by

Lee R. Reid et a1, assigned to the assignee of the present application,and incorporated in the present application by reference. At thisjuncture it should be explained that the choice of pellicle thickness isof importance, as above implied, in determining the bandwidth and theneed for a compensator plate. Using the pellicle described in theabove-identified copending application, bandwidth extending through theinfrared region and to long wavelengths of 100 microns or more can beachieved without requiring the use of a compensator plate.

From FIGS. 1 and 2, it can be seen that a plurality of reflectivestripes, numbered 1. to 9, of varying widths, are spaced at variousdistances on the thin film pellicle 11. For convenience, the pelliclespaces between stripes are numbered 1a to 9a, each space respectivelycorresponding in number to one of the reflective stripes. For uses ininterferometers and the like, for example, it is important that thestripes 1 to 9 be made reflective on both from the front and rear sidesof the beamsplitter. To achieve the required reflectivity, thereflective stripes may be constructed, for example, by firstconstructing a mask having a number of openings each of a sizecorresponding to the size of a desired stripe, next placing the maskupon the pellicle so that the openings correspond to the desiredpositions of the stripes and finally, subjecting the mask to a vapor ofa reflective metal such as gold, silver, or aluminum to deposit a metalband of a few hundred Angstroms thickness onto the pellicle.

The beamsplitter, in conjunction with a pair of high reflective mirrors,may then be used in an interferometer, as shown diagrammatically in FIG.3. To be understood is that the term mirror as used herein refers to afront surface or front reflecting mirror. Such front reflecting mirrormay be a sheet of glass coated with a reflective material such as gold,silver, aluminum, or the like on that surface of the glass on which abeam of light first impinges. Further to be emphasized is that thereflecting surface of such a mirror must be optically flat, i.e. thesurface must be a true plane, for otherwise, error would be introducedinto the measurements made since interferometers deal with ray errors orphase differences on the order of one ten billionth of a meter.Accordingly, for a definite guideline, it is generally considered thatthe term optically flat" means flat within a tolerance of one-tenthwavelength of the shortest wavelength of interest.

Light rays 12 entering the interferometer, are essentially parallel asif from a light source at infinity, and strike the beamsplitter at anangle of about 45 to the plane of the beamsplitter. As the wavefront ofthe rays is divided at the beamsplitter, as above explained, part ofsaid wavefront passes through the transparent areas 1a-9a of thebeamsplitter to strike the reflective surface of the mirror 13, and partof said wavefront is reflected from stripes 1-9 of the beamsplitter tostrike the reflective surface of the mirror 14.

The mirror 13 is positioned at an angle, P such that the portions of thewavefront which are transmitted through the transparent areas la-8a ofthe beamsplitter are reflected onto the back side of stripes 2-9. Theback sides of the stripes, being reflective as already described, directthe portions of wavefront reflected from mirror 13 onto lens 15, whichfocuses them onto a detector 16, to be further processed, as desired, byprocessor 17. The mirror 13 is movable away and toward the beamsplitteras shown by the arrow, thus enabling the portions of the wavefrontpassing through the pellicle to be changed in phase from those reflectedto mirror 14.

In a similar manner, the mirror 14 is disposed at an angle, P such thatthe portions of the wavefront which were first reflected from the frontsides of stripes l-9 are reflected a second time by the mirror 14 topass through the transparent areas 1a-9a of the beamsplitter in thedirection of the lens 15 to be focused upon the detector 16. To beunderstood is that, in general, angles 1' and 1' will be equal, but forcomplete description, the angles are referred to as being different.

Because of the geometrical relationship between the beamsplitter and thereflectivesurfaces of the mirrors 13 and 14, the stripes 1-9 depositedon the pellicle must be of different widths, each at a different spacingwith relation to one another. The reason for these varying sizes andspaces can best be explained with reference to FIG. 4 in which theangles and sizes have been greatly exaggerated to illustrate thegeometrical principles involved. From FIG. 4 it can be seen that rayswhich pass through the transparent portions 1a and 7a of thebeamsplitter strike the reflective surface of the mirror l3, and areeach reflected at the angle 20, which is twice the angle of thereflective surface 13 from a plane perpendicular to the direction oftravel of the light waves. In order that all of the light reflected fromthe reflective surface of the mirror 13 impinge upon the back sides ofstripes 2 and 8 to be reflected to the detector, the light ray passingjust on top of stripe 1 must be reflected from the mirror 13 to justimpinge on the bottom edge of the back side of he stripe 2. Likewise,the light ray passing just above the stripe 7 must be reflected from themirror 13 to impinge just on the bottom edge of stripe 8. Since themirror 13 reflects both of the light rays incident upon it at the sameangle, and since the distance for the light ray passing through opening7a to reflective surface 13 (denoted by the symbol i the height abovethe horizontal path of the light beam when the reflected beams againstrike the beamsplitter will be less for the beam passing throughopening 7a than for the beam passing through la. Geometrically, it canbe seen that each of the respective beams will be reflected upwards adistance 1 20, (assuming 6 to be very small) and since is smaller thanl, for all the light passing through opening 7a to impinge of the backside of stripe 8, stripe 8 must be mounted on the pellicle at a distancefrom stripe 7 which is smaller than the distance stripe l is from stripe2. Since the transparent spaces 1a-9a are of decreasing width, so mustthe stripes 1-9 in order that all the light which passes through thespaces shall fall upon the back side of the stripes.

Similar consideration should be given the reflecting light waves fromthe reflective surface 14. In order for the light waves reflected fromthe mirror 14 to emerge from the beamsplitter in a path parallel to thelight waves reflected from the back sides of the stripes, the mirror 14must be disposed at the same angle 0 as the mirror 13, so that lightwaves reflected from the stripe 1, for example, will pass through thetransparent space 1a after being reflected from the mirror 14. From theabove discussion of the size and spacing requirements imposed by themirror 13, it is concluded that the sizes and spaces must be ofdecreasing size as the distance between the mirror 13 and thebeamsplitter is decreased. Therefore, the space 1a must be of sizesmaller than stripe 1, the same being true of all the other stripes andassociated spacings.

The above discussion implies that the actual number and size of thestripes and their associated spacings effect the most efficientoperation. The following stripe sizes and spaces are illustrated for apellicle of the kind shown in FIGS. 1 and 2.

A beamsplitter having stripes and spacing of such dimensions as abovewould be used in conjunction with reflecting surfaces such as reflectingsurfaces of the mirror 13 and 14 shown in FIG. 3, each reflectingsurface being spaced at about 1.9 inches from the geometrical center ofthe beamsplitter, and being disposed at an angle of about 1 53 iron aplane perpendicular to the direction of travel of the light wavesimpinging upon it.

It should also be emphasized that the above dimensions, thoughillustrative, are arbitrary and given only by way of example. Theprimary purpose for setting forth the above date is to visualize therelative size relation between the stripes and spaces. For example, anyone arbitrary stripe or space could be chosen, and from the relationabove given, the rest of the stripes and spaces can be determined.Furthermore, the reflective surface need not be restricted to stripes,but could be, for example, of checkerboard, or other suitable pattern.

In interferometer spectrometer applications, it is necessary for one ofthe reflective surfaces 13 or 14 to be movable with respect to thebeamsplitter in order to change the phase of one of the two beamscreated by the beamsplitter, so that the beams of different phase, whenrejoined at the detector, will either additively or subtractivelyinterfere to increase or decrease respectively, the amplitude of thelight upon the detector. It can be seen, therefore, that very smallmovements of reflective surface 13 may cause large changes in amplitudeof the detected light output. The device, then, can be used for verydelicate and sensitive measurements.

Unlike amplitude division beamsplitters where the efficiency isdependent, in part, on the ability of the beamsplitter to pass part ofthe beam and reflect part of the same beam, the present invention reliesonly on the reflective properties of the beamsplitter for its operation,the beams impinging upon the transparent portions of the beamsplitterbeing unaffected since those beams only and totally pass through thetransparent portions, nothing being reflected. In other words, whereasthe amplitude division beamsplitters performed both reflecting andtransmitting functions on the incident beams simultaneously, thebeamsplitter of the invention performs only one function at a time:reflecting all of a given portion of the incident beam from the front orback sides of reflective stripes l9 or transmitting in all of adifferent portion of the incident beam through transparent areas la-9aof the beamsplitter pellicle, as shown in FIG. 4. Hence, since all thelight beams are directed in the desired direction by the entirelytransmitting and entirely reflective portions of the beamsplitter,substantially no light is wasted.

It can be seen, also, that the efficiency of the beamsplitter of theinvention is dependent on the amount of light reflected from surface 14which misses or does not impinge on transparent areas la-9a to betransmitted therethrough to the detector, and, also, on the amount oflight from reflective surfaces 13 which misses the back sides ofreflective strips 1-9 to be transmitted to the detector. These lossesincrease as mirror 13 is moved in operation of the interferometer, butthe losses are very small in comparison to the losses involved in thepreviously used amplitude beamsplitters; the theoretical efficiency ofan interferometer as shown in FIG. 3 can be made to approach 100percent.

Also, because the beamsplitter operates only on the theory ofreflection, the primary limitation on its bandwidth is the thickness andtransmittance of the thin film pellicle. As mentioned, above, a pellicleon the order of 0.5 micron in thickness will pass light wavelengths fromthe visible through the infrared range and to wavelengths up to andbeyond 100 microns. Furthermore, because the pellicle is so thin, theamount a beam is offset in passing through it is very small; hence, acompensator plate is not required to correct the beam. It must beemphasized, however, that in the interferometer applicationscontemplated, the pellicle and reflective stripes thereon must be of thesame optical flatness as the above described front reflecting mirrors.

Because of the particular ability of the beamsplitter of the inventionto pass light waves in the infrared region, of special importance areits applications in interferometer spectrometers, devices which are usedto determine electromagnetic spectra using conventional interferometertechniques. Such spectrometers may be used, for example, for determiningthe composition of the atmosphere of the earth by placing aninterferometer spectrometer in a satellite, measuring the spectrum oflight radiated from the surface of the earth, and determining whichwavelength of light is absorbed by the atmosphere. By such analysis,together with the knowledge of the absorption characteristics of each ofthe various elements, the composition of the atmosphere can be veryaccurately determined both as to whether certain elements exist in theatmosphere and the quantities of those elements which do exist. Ofparticular importance are measurements in the infrared light range sincethe majority of radiation from the earth are in the infrared region, andwhich, as above explained, presently used interferometer spectrometerscannot analyze for lack of a beamsplitter capable of handling infraredlight waves. The beamsplitter of the present invention, however,overcomes this problem, since it is capable of passing the wavelengthsof at least one hundred microns. An additional advantage of thebeamsplitter of the invention is that, because it is either entirelyreflecting or entirely transmitting, it is practically free from errorsintroduced by non-linear wave transmission across its intendedbandwidth. This is of importance especially in accurately determiningthe intensity of the received spectral lines in detennining the amountof the element present.

Although the invention has been described and illustrated with a certaindegree of particularity, it is understood that the present disclosurehas been made only by way of example and that numerous changes in thedetails of construction and the combination and arrangement of parts maybe resorted to without departing from the spirit and the scope of theinvention as hereinafter claimed.

What is claimed is:

l. A beamsplitter processing device comprising a. a light detectormeans,

b. a substrate having at least one area reflective on both sides and atleast one area transparent from both sides, such that light impinging onsaid substrate will be divided into a first beam reflected from saidreflective area and a second beam transmitted through said transparentarea,

0. a first reflecting means positioned to reflect said first beam oflight through said transparent area in the direction of said lightdetector means,

d. a second reflecting means positioned as to reflect said second beamof light onto the back side of said reflective area of said substrate,such that said second beam is reflected by said reflective area of saidsubstrate in the direction of said light detector means, said secondreflecting means being movable towards and away from said substrate,

e. whereby when said second reflective means is moved, the lightamplitude at said light detector means is changed.

2. A beamsplitter processing device comprising:

a. a transparent substrate;

b. a plurality of stripes, each of a different width, each of saidplurality of stripes being reflective on both sides, and affixed to saidtransparent substrate whereby successive stripes are separated bytransparent areas of said substrate, each of said areas being of adifferent width;

0. a first reflecting surface positioned to reflect substantially all ofthe light reflected from one side of each of said stripes, back througha transparent area of said substrate adjacent each of said stripes,

. a second reflecting surface positioned to reflect substantially all ofthe light transmitted through each of said transparent areas of saidsubstrate back onto the other side of each of said stripes, adjacentrespective transparent areas, said second reflective surface beingmovable toward and away from said transparent substrate, and

e. means to detect the amplitude of the combined light reflected fromsaid other side of said stripes and the light reflected from said firstreflective surface passing through said transparent areas of saidsubstrate.

3. A beamsplitter processing device comprising:

a. a quartz mounting ring positioned at an angle of about 45 to thedirection of travel of an impinging light wave;

b. an optically flat pellicle of a nitrocellulose material of thicknessbetween 0.3 and 3.1 microns mounted on said quartz mounting ring;

c. nine optically flat reflecting stripes of gold deposited (1. a firstoptically flat front reflecting mirror spaced 1.9

inches from the geometrical center of the quartz mounting ring, theangle of the plane of said first reflecting mirror being 43 07 from theplane of the pellicle, whereby light reflected from the front side ofeach of said stripes is reflected by said first mirror onto said spacesadjacent each of said stripes;

e. a second optically flat front reflecting mirror movable toward andaway from said quartz mounting spaced 1.9 inches from the geometricalcenter of the quartz mounting ring, the angle of the plane of the secondreflecting mirror being 43 07 from the plane of the pellicle, wherebylight first impinging on respective spaces between said stripes istransmitted therethrough to said second mirror thereby to be reflectedby said second mirror onto the back side of respective stripes adjacentsaid spaces;

. a light gathering lens in the path of the light beams reflected fromthe back side of said stripes and transmitted through said spaces afterfirst having been reflected from said first mirror;

g. a light sensitive detector spaced from said light gathering lens suchthat the light output from the lens strikes said detector;

h. whereby movements of said second mirror toward or away from saidmounting ring a measured distance produces a proportional change inamplitude of light falling on said light sensitive detector.

4. A beamsplitter light processing device comprising in combination:

a. a transparent substrate;

b. a source of light impinging upon one surface of said substrate;

c. a plurality of spaced stripes selectively affixed to said substratehaving selectively variable widths and being selectively reflective onboth sides, said stripes being separated by transparent areas of saidsubstrate with said transparent areas having selectively variablewidths;

d. first means for detecting amplitude characteristics of the lightpassing through said transparent areas of said substrate;

e. second means for directing light impinging on said transparent areastoward said first means; and

f. third means for directing light impinging on one surface of saidstripes toward said first means; whereby combination:

a. mounting means having a transparent pellicle afiixed thereto;

b. a source of light impinging upon one surface of said pellicle;

c. a plurality of spaced stripes selectively affixed to said one surfaceof said pellicle having selectively variable widths and beingselectively reflective on both sides, said stripes being separated bytransparent areas of said pellicle with said transparent areas havingselectively variable widths;

d. light detecting means for producing signals representing selectedoptical characteristics of the light passing through said pellicle;

e. first movable means for directing light impinging on said one surfaceof said pellicle and passing through said transparent areas toward saidstripes, whereupon said light is reflected toward said light detectingmeans; and f. second movable means for directing light impinging oncombination:

a. a mounting ring of quartz having a transparent pellicle ofnitrocellulose material affixed thereto;

b. a source of light impinging upon one surface of said pellicle;

c. a plurality of spaced stripes selectively affixed to said one surfaceof said pellicle having selectively variable widths and beingselectively reflective on both sides, said stripes being separated bytransparent areas of said pellicle with said transparent areas havingselectively variable widths;

d. means for detecting amplitude characteristics of the light passingthrough said transparent areasof said pellicle;

e. first means for directing light impinging on said one surface of saidpellicle and passing through said transparent areas toward saiddetecting means; and

f. second means for directing light impinging on said one surface ofsaid pellicle and reflected by said stripes toward said detecting means;whereby g. said detecting means produces signals representing selectedoptical characteristics of the light impinging on said transparent areasand the light impinging on said stripes.

1. A beamsplitter processing device comprising a. a light detectormeans, b. a substrate having at least one area reflective on both sidesand at least one area transparent from both sides, such that lightimpinging on said substrate will be divided into a first beam reflectedfrom said reflective area and a second beam transmitted through saidtransparent area, c. a first reflecting means positioned to reflect saidfirst beam of light through said transparent area in the direction ofsaid light detector means, d. a second reflecting means positioned as toreflect said second beam of light onto the back side of said reflectivearea of said substrate, such that said second beam is reflected by saidreflective area of said substrate in the direction of said lightdetector means, said second reflecting means being movable towards andaway from said substrate, e. whereby when said second reflective meansis moved, the light amplitude at said light detector means is changed.2. A beamsplitter processing device comprising: a. a transparentsubstrate; b. a plurality of stripes, each of a different width, each ofsaid plurality of stripes being reflective on both sides, and affixed tosaid transparent substrate whereby successive stripes are separated bytransparent areas of said substrate, each of said areas being of adifferent width; c. a first reflecting surface positioned to reflectsubstantially all of the light reflected from one side of each of saidstripes, back through a transparent area of said substrate adjacent eachof said stripes, d. a second reflecting surface positioned to reflectsubstantially all of the light transmitted through each of saidtransparent areas of said substrate back onto the other side of each ofsaid stripes, adjacent respective transparent areas, said secondreflective surface being movable toward and away from said transparentsubstrate, and e. means to detect the amplitude of the combined lightreflected from said other side of said stripes and the light reflectedfrom said first reflective surface passing through said transparentareas of said substrate.
 3. A beamsplitter processing device comprising:a. a quartz mounting ring positioned at an angle of about 45* to thedirection of travel of an impinging light wave; b. an optically flatpellicle of a nitrocellulose material of thickness between 0.3 and 3.1microns mounted on said quartz mounting ring; c. nine optically flatreflecting stripes of gold deposited upon both sides of said pellicle,said strips being, respectively, of widths 0.090, 0.103, 0.118, 0.135,0.154, 0.176, 0.201, 0.228, 0.259 inch with respective spacestherebetween of 0.084, 0.096, 0.110, 0.126, 0.144, 0.165, 0.188, 0.214,and 0.243 inch; d. a first optically flat front reflecting mirror spaced1.9 inches from the geometrical center of the quartz mounting ring, theangle of the plane of said first reflecting mirror being 43* 07'' fromthe plane of the pellicle, whereby light reflected from the front sideof each of said stripes is reflected by said first mirror onto saidspaces adjacent each of said stripes; e. a second optically flat frontreflecting mirror movable toward and away fRom said quartz mountingspaced 1.9 inches from the geometrical center of the quartz mountingring, the angle of the plane of the second reflecting mirror being 43*07'' from the plane of the pellicle, whereby light first impinging onrespective spaces between said stripes is transmitted therethrough tosaid second mirror thereby to be reflected by said second mirror ontothe back side of respective stripes adjacent said spaces; f. a lightgathering lens in the path of the light beams reflected from the backside of said stripes and transmitted through said spaces after firsthaving been reflected from said first mirror; g. a light sensitivedetector spaced from said light gathering lens such that the lightoutput from the lens strikes said detector; h. whereby movements of saidsecond mirror toward or away from said mounting ring a measured distanceproduces a proportional change in amplitude of light falling on saidlight sensitive detector.
 4. A beamsplitter light processing devicecomprising in combination: a. a transparent substrate; b. a source oflight impinging upon one surface of said substrate; c. a plurality ofspaced stripes selectively affixed to said substrate having selectivelyvariable widths and being selectively reflective on both sides, saidstripes being separated by transparent areas of said substrate with saidtransparent areas having selectively variable widths; d. first means fordetecting amplitude characteristics of the light passing through saidtransparent areas of said substrate; e. second means for directing lightimpinging on said transparent areas toward said first means; and f.third means for directing light impinging on one surface of said stripestoward said first means; whereby g. said first means produces a signalthat represents the relative optical characteristics of the lightimpinging on said transparent areas and the light impinging on said onesurface of said stripes.
 5. A beamsplitter light processing devicecomprising in combination: a. mounting means having a transparentpellicle affixed thereto; b. a source of light impinging upon onesurface of said pellicle; c. a plurality of spaced stripes selectivelyaffixed to said one surface of said pellicle having selectively variablewidths and being selectively reflective on both sides, said stripesbeing separated by transparent areas of said pellicle with saidtransparent areas having selectively variable widths; d. light detectingmeans for producing signals representing selected opticalcharacteristics of the light passing through said pellicle; e. firstmovable means for directing light impinging on said one surface of saidpellicle and passing through said transparent areas toward said stripes,whereupon said light is reflected toward said light detecting means; andf. second movable means for directing light impinging on said onesurface of said pellicle and reflected by said stripes toward saidtransparent areas, whereupon said light passes through said transparentareas and impinges on said light detecting means.
 6. A beamsplitterlight processing device comprising in combination: a. a mounting ring ofquartz having a transparent pellicle of nitrocellulose material affixedthereto; b. a source of light impinging upon one surface of saidpellicle; c. a plurality of spaced stripes selectively affixed to saidone surface of said pellicle having selectively variable widths andbeing selectively reflective on both sides, said stripes being separatedby transparent areas of said pellicle with said transparent areas havingselectively variable widths; d. means for detecting amplitudecharacteristics of the light passing through said transparent areas ofsaid pellicle; e. first means for directing light impinging on said onesurface of said pellicle and passing through said transparent areastoward said detecting means; and f. second means for diRecting lightimpinging on said one surface of said pellicle and reflected by saidstripes toward said detecting means; whereby g. said detecting meansproduces signals representing selected optical characteristics of thelight impinging on said transparent areas and the light impinging onsaid stripes.